The present invention relates to an adaptive receiving device removing interference from other users by an antenna directivity control, more particularly to an adaptive receiving device for a CDMA (Code Division Multiple Assess).
In such a cellular mobile communication system, interference from other users and interference by delay waves are the dominant factors which determine a receiving quality. Methods for removing these interference by employing adaptive antennas are considered. On the other hands, a CDMA method which can be expected for capacity acceptable for a large subscribership is noted as a wireless transmission method. A method utilizing a spread process gain is proposed as a receiving device employing an adaptive antenna which is suitable for a CDMA method.
Conventionally, for this type of an adaptive receiving device for a CDMA, as indicated, for example, in Oh, Kohno and Imai: xe2x80x9cAn TDL adaptive array antenna using spread process gain for spectrum spread multi-dimension connectionsxe2x80x9d, Communication Engineering Theory, Vol.J75-BII No. 11, pp. 815-825, 1992, and in Tanaka, Miki and Sawahashi: xe2x80x9cCharacteristic of decision feedback-type coherent adaptive diversity in DS-CDMAxe2x80x9d, Communication Engineering Technical Report, RCS96-102, 1996-11, the effect of SINR improvement due to process gain in an adaptive control is obtained by utilizing weight control error signal taken after de-spreading upon an antenna weight controlling.
FIG. 7 is a block diagram showing an example of conventional CDMA adaptive receiving devices, and FIG. 8 is a block diagram showing an adaptive receiving sub-block 27m for the m-th path in an adaptive receiving device for a CDMA of FIG. 7. Here, an adaptive receiving device for a CDMA is represented in the case where the number of receiving antennas is N (N is an integer more than 1), the number of users is K (K is an integer more than 1), and the number of multi-path is M (M is an integer more than 1).
Each of receiving antenna 11xcx9c1n made of N pieces receives solicitation wave signals and a plurality of interference wave signals which are code-multiplexed. Receiving antenna 11xcx9c1n are arranged closely so that each receiving signal has the correlation with each other. The first adder 5 adds outputs of adaptive receiving sub-blocks 271xcx9c27M for the firstxcx9cthe M-th path, and outputs the k-th user demodulation signal. The decision circuit 6 performs hard decision for the first adder 5, outputs the k-th user decision symbol.
The adaptive receiving sub-block for the m-th path is composed of the weighted synthesis circuit 7, the first delay circuit 10, the de-spreading circuit 11, the demodulation circuit 12, the third complex multiplier 15, the error detection circuit 16, the fourth complex multiplier 17, the second delay circuit 18, the third delay circuit 19 and the antenna weight control circuit 20.
The adaptive receiving sub-block 27m for the m-th path inputs antenna receiving signal 1xcx9cantenna signal N and the k-th user decision symbol which is an output outputted from the decision circuit 6.
The weighted synthesis circuit 7 is composed of the first 10 complex multiplier 81xcx9c8N and the second adder 9. A signal received by the m-th path inherent antenna directivity pattern is generated by multiplying antenna receiving signal 1xcx9cantenna receiving signal N by antenna weight Wm1 antenna WmN and by adding them.
The first delay circuit 10 delays an output outputted from the weighted synthesis circuit 7 on the basis of path delay of an separately required solicitation wave signal corresponding to multi-path. The de-spreading circuit 11 computes the correlation between an output of the weighted synthesis circuit 7 and a spread code Ck of the k-user. The modulation circuit 12 is composed of the transmission path estimate circuit 13 and the second complex multiplier 14. An output which is multiplied the de-spreading circuit 11 by a complex conjugate of transmission estimate output becomes an output of adaptive receiving sub-block 27m for the m-th path.
The third complex multiplier 15 multiplies the k user decision symbol by a transmission path estimate output. The error detection circuit 16 computes the difference between an output of the third complex multiplier 15 and an output of the de-spreading circuit 11, and detects detection errors. The fourth complex multiplier 17 multiplies a decision error by the k-user spread code Ck, and generates a weight control error signal. The delay circuit 18 delays weight control error signals on the basis of path delay of the foregoing separately required solicitation signal so as to cancel out the effect of the first delay circuit 10.
The third delay circuit 19 delays antenna receiving signal 1xcx9cantenna receiving signal N in accordance with the processing time of the weighted synthesis 7, the de-spreading circuit 11, the demodulation circuit 12, the error detection circuit 16 and the like. The antenna weight control circuit 20 computes antenna weight Wm1xcx9cWmN from a weight control error signal which is an output of the second delay circuit 18 and an output of the delay circuit 19.
By assuming a spread code Ck as a complex code composed of a code of CkI and a code of CkQ which are in an orthogonal relationship of the two (2) affiliations, the de-spreading circuit 11 can be realized by one-piece of complex multiplier and an averaging circuit over a symbol interval. Moreover, the de-spreading circuit 11 can be also realized by a transversal filter component in the case of assuming Ck as a tap weight.
In receiving signals from receiving antenna 11xcx9cN of N pieces, a solicitation wave signal component, an interference wave signal component and thermal noise are included. Moreover, multi-path component exists in a solicitation wave signal component and in an interference wave signal component respectively. Conventionally, those signal components arrive from different directions.
A conventional adaptive receiving device for a CDMA shown in FIGS. 7 and 8, prepares adaptive receiving sub-block 271xcx9c27M for the firstxcx9cthe M-th path independently with respect to multi-path components and performs weighted synthesis of a receiving signal in each weighted synthesis circuit 7 so as to make solicitation wave signal-to-interference wave signal power rate (SIR) of signal components of each path to be the maximum value. As a result, as for antenna gain with respect to the arrival directions (directivity pattern) of adaptive receiving sub-block 271xcx9c27M for the firstxcx9cthe M-th path, it is formed so that it becomes larger with respect to the respective arrival directions of path signal components and becomes smaller with respect to other delay wave signal components and interference wave signal components
In order to improve the deterioration of adaptive control characteristic of a conventional adaptive receiving device for a CDMA shown in FIGS. 7 and 8 in the case where the number of paths are large, the authors previously proposed an adaptive receiving device for a CDMA adding weight control error of all paths for each user (Japanese Patent Application No. H9-210336). This adaptive receiving device for a CDMA prepares a weighted synthesis circuit with respect to each user, and performs weighted synthesis of antenna weight and antenna receiving signal so as to make synthesis weight control error signal adding weight control error signal of all paths for each user to be the minimum value. As a result, one directivity pattern for each user is formed, antenna gain becomes larger with respect to the arrival directions of signal components of each path, and it becomes smaller with respect to the interference components. Since this method adds weight control error signals of all paths for each user, information of adaptive control becomes increasing, and its adaptive control characteristic is excellent even in the case where the number of paths is large.
Since a conventional adaptive receiving device for a CDMA shown in FIGS. 7 and 8 uses error signal independently in a unit of each path and forms independent directivity pattern, in the case of error signal of path of smaller power, the reliability is lowered by transmission path estimate error. Therefore, in the case where the number of paths is large, the adaptive control characteristic is deteriorated, particularly, it becomes the problem that the directivity pattern of path when it is smaller power is difficult to be formed.
As means for solving the problem, an adaptive receiving device for a CDMA adding weight control error of all paths for the above described each user is proposed, but when multi-path component of solicitation wave signal arrival angle difference is incorporated simultaneously, since the width of beam is broadened and excessive interference is also incorporated, interference suppression ability is deteriorated in the case where the arrival angle difference of multi-path is large.
Moreover, since a conventional adaptive receiving device for a CDMA forms different directivity pattern for each user, it is the problem that it is difficult to perform multi-user receiving which receives a plurality of signals of users as a unit.
An objective of the present invention is to provide an adaptive receiving device whose adaptive control characteristic and interference suppressive ability are excellent under circumstances where a large number of paths arrive from various angles.
The adaptive receiving device of the present invention forms a pattern simultaneously incorporating paths of given combinations from all multi-path of all users as a directivity pattern receiving each path of each user.
More particularly, the adaptive receiving device of the present invention comprises an adaptive receiving block for the firstxcx9cthe K-th user (21xcx9c2K of FIG. 1), an adaptive receiving sub-block for the firstxcx9cthe M-th path for each user (41xcx9c4M of FIG. 2), and one weight control error synthesis means (3 of FIG. 1).
In the present invention, weight control error signal is synthesized with respect to paths whose arrival directions are close each other, and performs a control without weight control error difference with respect to paths whose arrival directions are apart. Through these performances, the volume of information available for adaptive control can be increased, and excellent adaptive control characteristic and interference suppression ability are obtained. Moreover, by performing a control of synthesizing weight control error signals of a plurality of multi-user, a multi-user receiving can be easily realized.